First, what can happen if the spring and pump are poorly matched is the spring will not have enough tension and will compress before the pump starts moving down into the cavity. Then you get a hesitation because the pump won't start pumping until the spring has bottomed out. So the spring has to be strong enough to ensure the pump starts moving first before the spring starts compressing. That's why the spring we use the most has thick coils to be strong enough, but not so many coils that it will go into coil bind.
Metering Rod Hangers
Image 18 shows a selection of hangers for the metering rods. As we move down the picture, the hole location in the hangers move down as well. The hangers are sorted by a letter that's stamped on them, and basically, the higher the hole, the higher the letter. It starts at "B" and goes all the way down to "Y" and each moves the hole in an increment of 0.005-inch.
One way to take advantage of this is, say when the secondaries begin to open you have an overly rich condition. You can use the hanger to locate the metering rod down deeper into the jet, and that will lean out the initial fuel curve as the secondaries begin to open. So, combine that with the different styles of metering rods with the different tapers and you can just about come up with any type of fuel curve that you need.
Well, there you have it. Take these tips to the shop and start really tuning on that carb and we'll see you in Victory Lane!